Various cordless electrical devices may be powered by a battery pack. Examples of such cordless electrical devices include, but are not limited to, laptop computers, cell phones, personal digital assistants, and power tools such as a drill. The battery pack may include a plurality of battery cells and power switches to allow the battery cells to either supply current (discharge operation mode) or to be charged (charge operation mode). The battery pack may also include battery state monitoring circuitry powered by the battery cells to perform of number of tasks to maintain a safe and desired use of the battery cells.
In a conventional battery pack, a current sense resistor may be utilized in series with the battery cells of the battery pack to provide a signal to the battery state monitoring circuitry representative of current from or to the battery cells. The use of the current sense resistor may be acceptable for low current applications. However, for high current applications the current sense resistor may cause excessive power dissipation. In addition, the current sense resistor contributes an additional component and connection cost. Accordingly, there is a need to provide for battery pack current monitoring without using a current sense resistor.